Forced-flow boiler with a plurality of resuperheating stages



March 30, 1965 H. BACHL 3,175,542

FORCED-FLOW BOILER WITH A PLURALITY OF RESUPERHEATING STAGES Filed Feb. 14, 1958 2 Sheets-Sheet l H MED/UM PRESSURE HIGH pzssuee F REJl/PEBHEATER '1 FINAL .s'z/PEQHEATEE 1 LOW Jl/PEP/IEATEE STEAM Ol/7ZE7' 755 PEi/NJECT/ON 13 BUR/V51? PLANE FEED WATER INLET I l Fig.1 Fig.2

2 Sheets-Sheet 2 H. BACHL March 30, 1965 FORCED-FLOW BOILER WITH A PLURALITY 0F RESUPERHEATING STAGES Filed Feb. 14, 1958 Fig. 3

United States Patent Filed Feb. 14, 1958, Ser. No. 768,511 4 Claims. (Cl. 122-479) My invention relates to forced-flow steam generators of the once-throng type wherein the feed water is heated, evaporated and superheated in one passage through a continuous tube system without storage drums. In a more particular aspect, my invention concerns forcedfiow generators with at least two resuperheating stages located between the feed-Water receiving evaporator stage and the final superheating stage of the plant.

Such forced-flow steam generators with two resuperheating stages have heretofore been designed, in analogy to boilers with a single resuperheating stage, so that both resuperheating stages and the final superheating stage were distributed over the entire flue cross-section but were located in different-temperature ranges. With such a generator design, the high-pressure final temperature of the superheated steam generated can be regulated by injection of water, and the temperature of one of the resuperheaters or reheating super-heaters can be regulated,

for example by flue damper flaps, so that these temperatures remain at an approximately constant value within a given load range of the generator. However, it is not feasible in' this manner to thus regulate all three temperatures of the steam leaving the outlets of the three respective superheaters, without adding heat exchangers or water injection devices to the two resuperheaters.

These shortcomings of multiple-stage superheating plants for forced-flow generation of steam are aggravated if they manifest themselves after erection and operation of a boiler plant so that a very costly and time-consuming renovation of the plant is necessary.

It is an object of my invention to eliminate the abovementioned shortcomings.

To this end, and in accordance with a feature of my invention, I apply an output-temperature regulation to each of the three or more superheating stages from the firing side of the plant as will be more fully set forth hereinafter.

With drum-type boilers, it has already been attempted to'provide for indirect heating of a resuperheater within a separate firing chamber. Such a temperature regulation, however, cannot readily be employed with a forced-flow steam generator which has a continuous duct path traversed only once by a quantity of water forced through the path and converted to steam and superheated on a single passage. This is so because the water quantities, the output temperatures at the individual stages of the plant, and the heating power supplied to the plant, have a direct influence upon one another. According to my invention, however, such indirect heating of a plurality of resuperheaters in a forced-flow steam generator is economically achieved.

According to a feature of my invention, the flue-gas path of the forced-flow boiler plant is subdivided in the combustionchamber into three or more flue portions with separate burners. Furthermore, the high-pressure final superheater, the medium-pressure resuperheater, and the low-pressure resuperheater and, as the case may be, further superheating surfaces are correlated to thesecomponent flows of fire gases so that a portion of the superheater in each of the respective pressure stages is located in a separate burner-and-flue compartment which permits regulation of the heat supply at the fire side of the system.

The heating surfaces of the high-pressure evaporator system which are traversed by water or steam of low "ice temperature, are preferably distributed approximately uniformly into the parallel related flue compartments, and the steam-traversed parallel lines of the evaporator are made to merge with one another before entering into the final superheater common to all parallel evaporator portions.

However, according to another feature of the invention, the supply of water may also be controlled in the usual manner in dependence upon the'loading imposed upon the steam generator, such regulation acting on the supply of water for the entire boiler plant; whereas the feeding of water from the common sup'ply' into the respective component systems is distributed in such a manner that the output temperature of each superheater stage is regulated primarily from the appertaining burner-and-flue compartment, and any necessary equalization of temperature departures in the individual component systems is effected by injection of water into the high-pressure portion.

The foregoing and other objects and features of the invention will be apparent from the following description of the embodiments illustrated on the drawings in which:

FIGS. 1 and 2 show twocross-sectional views in mutually perpendicular, vertical planes of a forced-flow gerierator accord-ing to the invention in simplified illustration, FIG. 1 being a section taken along line I-I of FIG. 2, and FIG. 2 being a section taken along line II-II of FIG, 1. V

FIG. 3 is a circuit diagram of the same boiler plant.

In the illustrated embodiment, the steam generating boiler is subdivided into three individual boilers I, II, III. Up to the final superheater stage, the heating surfaces traversed by waterand steam of low temperature are subdivided into parallel lines. The subdivision is such that each of the three component boilers is supplied with approximately the same quantity of feed water. The boiler is subdivided into three separate firing chambers by two partitioning walls indicated in FIG. 3 by the two vertical dot and dash lines. Each of these three chambers possesses its own firing system, its own feed-water circulation, and its own combustion-gas flue conduit, so that each of the three individual firing systems can be regulated by varying the supply of fuel and feed water.

Each of the three firing chambers is equipped with superheater surfaces in addition to the heating surfaces for pre-heating, evaporation, and pre-superheating. The final superheater common to all three firing systems is mounted in one of the three firing chambers. The highly superheated steam in the final superheater is supplied to the high-pressure stage of a turbine plant fed from this boiler plant so as to be used as fresh steam, the turbine plant having a high-pressure, a medium-pressure and a low-pressure portion. For avoiding moisture in the low pressure turbine of the plant, the steam is twice resuperheated. The first resuperheating takes place after the steam leaves the high-pressure stage, in a medium-pressure resuperheater or reheating superheater 22. The second resuperheating occurs after a further drop in temperature and pressure which occurs in the medium-pressure stage of the turbine. This second heating is effected in the low-pressure resuperheater or reheating superheater 23, before the steam is supplied to the low-pressure stage of the turbine. Consequently, the pressure in the superheaters continuously decreases, while being accompanied by increase in steam volume, from the high-pressure superheater 21 through the first resuperheater 22 to the second resuperheater 23.

The final superheater 21 is located in only one of the three component boilers, namely in the boiler denoted by II. The two resuperheaters 22 and 23 are located in the two other component boilers I and HI.

and 23 respectively,

As apparent from the diagram of FIG. 3, the feed water coming from the feed-water reservoir is preheated in low-pressure preheaters 6. The supply of preheated water is controlled and regulated in accordance with the required feed-water quantity by means of pumps 7 whose speed of revolution is controlled accordingly. The pumps 7 force the feed Water through the high-pressure preheaters uniformly into the component boilers I, II and III. The fine regulation of the individual boilers I, II and III is efiected by throttle valves 9 which are designed as single-seat valves or regulating valves. By means of these valves, the feed water supply to each boiler can be varied independently of the other boilers. The quantity of feed water passing to the individual boilers is measured with the aid of known measuring diaphragms located at 10. The feed Water thence passes in sequence through the heating surfaces of the following boiler components in each stage:

First the Water passes through a screening member 11 at the bottom of the boiler, then along the front-wall firing chamber 12, then along meander-shaped paths extending first along the side wall 14 and the rear wall 15, and thereafter. also along the front wall 13 of the boiler.

Since the end temperature of the three individual boilers is supposed to be equal, a Water injection unit 16 is provided which commences to operate when the desired temperature, for instance 510 C., is exceeded. Such water injection devices are knownas such. 7

For starting the steam generating operation, the plant is provided with a starter line 17 with starter valves 18 which are designed as high-pressure slide valves. The steam-Water mixture occurring during the starting period is discharged through the valves 18 and the line 17.

The quantities of steam produced, during normal operation in respective boiler 1,11 and II pass through respective valves 19 and then merge in a line or duct means 20 common to all component boilers thus securing good mixing. v

The mixed steam then passes into the final superheater 21 whose heating surfaces are differently arranged. Merging ducts 30 extending from the respective steam generator starting lines 17 connect with the lines 20 and with each other, and additional ducts 31' connect the lines 20 with the final superheater 21, the merging ducts 30 and additional ducts 31 thereby collectively constituting interconnecting means for connecting the lines 20 to each other andto the final superheater. If after a long period of operation, a different heating of the heating surfaces occurs, for instance due to non-uniform deposition of soot, the temperature dilferences are equalized by subsequent injection of Water at 24.

At the exit of the final superheater 21, the temperature of the high-pressure steam, being above 600 vC., is measured and applied to a carbon-type regulator or burner control means 25 which regulates the fuel supply or burners in the combustion chambers of the boilers in dependence upon the departure of the exit temperature from the desired value.

Located in boilers I and III are the resuperheaters 22 to which the steam is supplied through lines 26. The temperatures of respective boilers I, III are regulated by means of Water-injection lines 27 if a nonuniform supply of heat to these superheaters occurs, for instance due to non-uniform deposition of soot.

During the above-mentioned starting period, cooling air is blown at 30 into the boiler for cooling the final superheater 21.

'The temperature regulation ofeach superheater stage is eifected essentially by performing a regulation in the appertaining combustion and flue chamber. Preferably boilers. Accordingly, three temperature-responsive regulating devices (25 in FIG. 3) or three regulatable pumps (7) are provided. Slight difierences in outlet temperatures are equalized by injection (24) ahead of the mixing point at the entrance of the steam into the final superheater.

It will be obvious to those skilled in the art, upon a study of this disclosure, that the invention is analogously applicable to forced-flow steam generating plants with more than two intermediate superheaters, and that plants according to the invention can be modified with respect to design features and circuitry without departing from the essential features of the invention and within the scope of the claims annexed hereto.

I claim:

1. A forced-flow steam generator for connection to a power load having a high pressure stage, a medium pressure stage and a low pressure stage, said generator comprising a final superheater and aplurality of reheating superheaters all having respectively difierent steam pressures, said final superheater being adapted to be connected to supply steam to said high pressure stage and said reheating superheaters being respectively adapted to be connected to reheat steam returned from said high pressure stage to said medium pressure stage and returned from said medium pressure stage to said low pressure stage so that a'flow path is defined from said final superheater to the high pressure stage and from the latter through one of said reheating superheaters to the medium pressure stage and from the latter through another of said reheating superheaters to the low pressure stage, combustion gas duct means having as many burner and flue compartments and evaporator sections as the generator has of said final superheater and said reheating superheaters, a portion of said final superheater and a portion of each'of said reheating superheaters being located in separate ones of said compartments and a corresponding one of said evaporator sections being located in one of said respective compartments, burner control means for individually regulating the heat supply from each of said compartments to said respective superheaters, and a plurality of outlet lines connecting said evaporator sections with each other in parallel, and interconnecting means connecting said outlet lines to each other and to said final superheater, said interconnecting means including a plurality of merging duct lines each connected to one of said evaporator sections, there being as many of said merging duct lines as the number of said final superheater and said reheating superheaters.

'stage to said low pressure stage so that afiow path is de- 2. A forced-flow steam generatonfor connection to a power load having a high pressure stage, a medium pressure stage and a low pressure stage, said generator comprising a number of separate boilerunits each having its own burner and flue compartments, each of said boilers having a feed water inlet and a high-pressure heating system including respective evaporator sections located in respective ones of said flue compartments and extending from said inlet and traversed, when in operation, by water and steam of a temperature below the generator 'outlet temperature, a finalsuperheater and a plurality of reheating superheaters all being adapted to operate at respectively different steam pressures, said final" superheater being adapted to be connected to supply steam to said high pressure stage and said reheating superheaters being respectively adapted to be connected to reheat steam returned from said high pressure stage to said medium pressure stage and returned from said medium pressure fined from said final superheater to the'high pressure stage and from the latter through one of said reheating superheaters to the medium pressure stage and from the latter through another of said reheating superheaters to the low pressure stage, said final superheater and said reheating superheaters being located in difierent ones of said respective flue compartments, said high-pressure heating systems having heating surfaces approximately uniformly distributed over said respective boilers and forming respective parallel paths, a steam conduit into which said paths merge with each other, said conduit having at one end thereof a plurality of merging duct lines each connected to one of said respective evaporator sections, the other end of said conduit being connected with said final superheater, and each of said boilers having burner control means for regulating the heating of said respective superheater.

3. A forced-flow steam generator according to claim 1, including water injetcion means located at said interconnecting means between each of said respective evaporator sections and said final superheater for compensating temperature differences of said respective evaporator sections.

4. A forced-flow steam generator according to claim 2, including feed-water supply means connected to said inlet and being controllable for adapting the total water supply to the loading of the generator, said steam conduit connecting and merging said systems at a merging location prior to said final superheater, said feed-water supply means including water injection means for injecting water into a respective boiler system substantially at said merging location of said systems so as to compensate for temperature differences of said respective systems.

References Cited in the file of this patent UNITED STATES PATENTS 2,032,391 Armacost Mar. 3, 1936 2,346,179 Meyer et al Apr. 11, 1944 2,669,977 Lewis Feb. 23, 1954 2,700,353 Schoenfeld Ian. 25, 1955 2,848,983 Lieberherr Aug. 26, 1958 2,864,343 Jenkins 'Dec. 16, 1958 2,939,286 Parlecka June 7, 1960 FOREIGN PATENTS 318,983 Switzerland Ian. 31, 1957 323,723 Switzerland Sept. 30, 1957 578,588 Canada June 30, 1959 OTHER REFERENCES Dauber: A Supercritical Pressure Plant, published in the August 1956 edition of Combustion (pages 47-56 relied on). Copy available in Scientific Library. 

1. A FORCED-FLOW STEAM GENERATOR FOR CONNECTION TO A POWER LOAD HAVING A HIGH PRESSURE STAGE, A MEDIUM PRESSURE STAGE AND A LOW PRESSURE STAGE, SAID GENERATOR COMPRISING A FINAL SUPERHEATER AND A PLURALITY OF REHEATING SUPERHEATERS ALL HAVING RESPECTIVELY DIFFERENT STEAM PRESSURES, SAID FINAL SUPERHEATED BEING ADAPTED TO BE CONNECTED TO SUPPLY TO SAID HIGH PRESSURE STAGE AND SAID REHEATING SUPERHEATERS BEING RESPECTIVELY ADAPTED TO BE CONNECTED TO REHEAT STEAM RETURNED FROM SAID HIGH PRESSURE STAGE TO SAID MEDIUM PRESSURE STAGE AND RETURNED FROM SAID MEDIUM PRESSURE STAGE TO SAID LOW PRESSSURE STAGE SO THAT A FLOW PATH IS DEFINED FROM SAID FINAL SUPERHEATER TO THE HIGH PRESSURE STAGE AND FROM THE LATTER THROUGH ONE OF SAID REHEATING SUPERHEATERS TO THE MEDIUM PRESSURE STAGE AND FROM THE LATTER THROUGH ANOTHER OF SAID REHEATING SUPERHEATERS TO THE LOW PRESSURE STAGE, COMBUSTION GAS DUCT MEANS HAVING AS MANY BURNER AND FLUE COMPARTMENTS AND EVAPORATOR SECTIONS AS THE GENERATOR HAS OF SAID FINAL SUPERHEATER AND SAID REHEATING SUPERHEATERS, A PORTION OF SAID FINAL SUPERHEATER AND A PORTION OF EACH OF SAID REHEATING SUPERHEATERS BEING LOCATED ING SEPARATE ONES OF SAID COMPARTMENTS AND A CORRESPONDING ONE OF SAID EVAPORATOR SECTIONS BEING LOCATED IN ONE OF SAID RESPECTIVE COMPARTMENTS, BURNER CONTROL MEANS FOR INDIVIDUALLY REGULATING THE HEAT SUPPLY FROM EACH OF SAID COMPARTMENTS TO SAID RESPECTIVE SUPERHEATERS, AND A PLURALITY OF OUTLET LINES CONNECTING SAID EVAPORATOR SECTIONS WITH EACH OTHER IN PARALLEL, AND INTERCONNECTING MEANS CONNECTING SAID OUTLET LINES TO EACH OTHER AND TO SAID FINAL SUPERHEATER, SAID INTERCONNECTING MEANS INCLUDING A PLURALITY OF MERGING DUCT LINES EACH CONNECTED TO ONE OF SAID EVAPORATOR SECTIONS, THERE BEING AS MANY OF SAID MERGING DUCT LINES AS THE NUMBER OF SAID FINAL SUPERHEATER AND SAID REHEATING SUPERHEATERS. 